Image scanners are used to convert information from one medium to another. For example, in document scanning the information on a document is converted from printed matter on a page to electrical signals for transmission to another unit, for information handling, for electronic storage, etc.
Charge coupled devices (CCD's) utilizing charge transfer technology are one modern application of technology useful in image scanners. Light is impinged on the photosites on a CCD device, the device detects this information and converts it to electrical signals for subsequent use. The familiar integrated cicuit structure on a chip of a few tenths of an inch by a few tenths of an inch (8 mm.times.8 mm) does not lend itself to CCD imager structure. If optics are eliminated, a CCD imager would have to be as wide as the page being scanned and located within several thousandths of an inch from the page to achieve adequate resolution. The cost of such a device would be extremely high because the manufacturing yield of such a large device would be very, very low. Thus, shorter CCD devices have been used but these have concomitant drawbacks. When several shorter CCD imagers are used to sense the same object line, the ends of the photosensor arrays overlap optically or mechanically or else a narrow stripe on the scanned page will be blank. Further, complicated optics for page width scanners must be utilized.
Use of small, dense, linear CCD imagers have also been shown with the use of reduction optics. However, when the size of the image device is reduced, the resolution suffers due to the limited number of available photosites. One method known to solve this problem is the use of CCD imagers with beam splitter optics. That is, the optics divide the scanned light information into two or more beams, one for each CCD imager, depending on the resolution desired. However, the cost is also very high in this technique due to added electronics and optics. One example of such a system is disclosed in Ser. No. 949,179, filed Oct. 6, 1978, now U.S. Pat. No. 4,272,684 and assigned to the same assignee.
According to the present invention, a high density CCD imaging array with a bilinear array of photosites on a single integrated circuit chip is utilized in an image scanning configuration. Offset photosites in two separated rows are coupled by transfer gates to four shift registers in a quadrilinear array. Registers for intermediate storage are included to allow the signals from the separate photosites to be stepped to the indicated shift registers. The outputs of these shift registers are multiplexed to generate a single output pulse train representative of the information scanned.